Not the dumbest thing I've ever done, but definitely on the list. I was changing the differential on my Mopar after successfully scrambling it while doing burnouts one afternoon, for no particular reason other than to see what would break first. Anyhow, there is an access hole in between the wheel studs allowing you to remove the axle retaining nuts with a socket and extention on a ratchet. For whatever reason that I can't explain, I stuck my finger into that access hole past the second knuckle and quickly realized it wasn't coming back out. There was a semi sharp edge on the backside of the hole that locked down and dug into the skin on my finger when I tried to remove it. There wasn't a nice chamfer like on the front. It could have been worse I guess because a friend came by to see how the job was going and after much laughter, verbal abuse and the confirmation of me being the jackass of the month, I did get a lift to the hospital. It was bleeding pretty good by the time I showed up in Emergency with the axle. The Triage nurse didn't think my condition was life threatening enough, so I sat in the waiting room for a few hours with the axle on my lap. It was somewhat embarassing and difficult to come up with creative answers after being asked a dozen times..."what happened to you?" Eventually, after waiting my turn and then soaking in ice water for a half hour and the use of some kind of lubrication and a flexible nylon sleeve inserted around my finger I was at last free, if not any wiser.